Manufacture of electric cables



M. KLEIN 2,001,065

MANUFACTURE OF ELECTRIC CABLES Filed Nov. 5. 1951 ay M,

Patented May 14, 1935 UNITED STATES PATENT OFFICE MANUFACTURE OF ELECTRIC CABLES Maurus Klein, Berlin, Frledrichshagen, Germany Applicatlonnlfovember 5, 1931, Serial No. 513,195

Germany 2 Claims.

of the partial capacities. In order to avoid such unbalancing, two conditions are required:

The two insulated conductors forming a pair must (I) be exactly equal and all the details of their insulation must also be the same;

. (II) occupy in the cable exactly equivalent positions relatively to the other conductors of the cable, including the lead covering.

The same conditions must be applied to two pairs of a set and generally to the co-ordinated elements of any quad formed by one twisting. In order to simplify the explanatory statement,

. the twisting of two conductors will always be referred to in the formation of a pair. The explanations also apply to other twistings and do not require any additional explanations.

Condition I is generally fulfilled with suflicient approximation.

The construction and the methods of operation of twisting machines are known. The two insulated conductors are wound on winding-0E bobbins arranged in the cage of the winding machine. They are drawn by the drum through the twisting draw plate, whilst at the same time the rotation of the cage round its shaft takes place. The bobbins drawn by the conductors begin also to rotate round their shaft and consequently the conductors are subjected to the drawing tension.

In order to fulfil condition II, the two insulated conductors must be symmetrically arranged around the axis of the pair. In order to comply with this condition, it is necessary to (III) symmetrically distribute the two conductors over the surface of the imaginarycone formed by the two conductors when joined together in the twisting draw plate;

(IV) take care that the drawing tension on each of the conductors passing through the draw plate should be of exactly the same value at any moment during the twisting operation.

Any difference in the tension would cause a difference in the length of the conductors of the pair produced by such twisting. Instead of twist- M'arcli' 3, 1931 ing the twoconductors uniformly one round the other, the less tensioned conductor would be twisted more or less uniformly round the other which is more powerfully stretched and more or less uniformly in a straight line. In an extreme 5 case the first conductor, namely the conductor which is stretched to a smaller extent, will become twisted in turns equal to the length of twist round the other, and the length of the former conductor will be about 1% greater than that of the latter, 10 in accordance with the difference in the lengths between the pair composed by the twisting of two conductors and that. of the component conductors. Such an asymmetrical pair would be abso-' lutely unusable and it is known from experience 15 that much smaller differences produce excessive unbalancing values. The importance of obtaining a perfect equality between the two tensions and the diificulties of the problem to be solved will readily be understood. '20

In order to regulate the tensions, the cable works have no other means at the present moment than to apply or release the brakes of the winding-01f bobbins. These brakes are regulated as carefully as possible. This method however, 25 does not offer a satisfactory solution of the problem, owing to the defects in the principle of the system. These defects are as follows:

. 1. The tension in the conductor is subjected to constant changes, partly periodical, due to causes 30 resulting from the very principle of the action' exerted by the regulation of. the brakes of the coils, but independent of the active power of the brakes.

It is possible to keep these changes between certain limits, but they cannot be sufficiently controlled to cause them to take place in concordance with the two conductors. Under such conditions there can never be any probability of 40 condition IV being complied with.

2. The adjustment of the bobbin brakes can be neither measured nor regulated with sumcient accuracy. Therefore, the same active power of the two brakes is obtained with a certain ap- 4 proximation only. The result will always be uncertain it the two tensions are more-or less diflferent, and it will never be possible to know the real difference, except by measuring the finished cable, when it is no longer possible to alter the 60 results obtained.

The object of this invention is to do away with these defects by applying any form of brakes exerting a direct action on the conductors to be twisted. The necessary tensions result from the not invariable.

Figure 1 is a diagrammatic showing of the direct braking action of this application. Figure 2 is a top plan view of a preferred form of brake.

The invention utilizes, with greater success, a brake called deformation'brake that is to say, a brake, the active braking power of which depends upon the resistance exercised by the insulated conductor against its own deformation,

for instance by bending. For this purpose it is' possible, for instance as Fig. 1 shows, to cause the insulated conducting wire F to pass between a certain number of grooved pulleys P in such manner that the wire embraces a part only of the circumference of each and the pulleys supporting in passing, small bends alternating on the right and on the'left.

Trials made with thesedeformation brakes on -insulated conductors and on pairs formed by insulating conductors, as used in the manufacture of telephonic cables, have shown that it is possible to cause with a limited number of pulleys, tensions of several kilogrammes and that the deformation necessary for the purpose in view has no effect, either on the conductors or on the insulation surface of the latter.

For a given twisting machine and a given conductor, the tension only depends-as in the case of all direct acting brakes-upon the active braking power, but the latter only depends upon the position of the pulleys. If the positions are secured by worms, toothed wheels or any other similar means, the chosen position of the pulleys will be stationary and consequently the tensions will also be stationary.

The brake may be formed, according to Fig. 2, by four pulleys (I, 2, I and l) two of which, the first and the last, being mounted on stationary shafts and the two others arranged on a disc 5 capable of rotating round its axle i by means of a worm I, so as to be able to alter the amount of deformation. For controlling the position of the worm and of the disc, use is made of scales: the scale of the worm has 100 divisions and that of the disc, 60. The zero positions correspond to a ,non-deformed conductor, in which the four pulleys I, 2, 3 and 4 touch the conductor F without deforming it. It is possible to increase the deformation by turning the disc 5 by means of the wheel 8 and to read to one half a division on the scale of the worm (3 angular measurement). The position of the disc 5 may thus be fixed with an exactitude to 1.8 minutes (corresponding to one division on the scale of the wheel 8). Two or more brakes of the same construction built with the accuracy of scientific mechanisms can easily be adjusted in such manner as to exercise the same deformation with perfect accuracy.

The extreme precision and stability of such deformation brakes render their adjustment possible, not only in regard to the same deformations, but also in regard to the same tensions, that is to say, for the same lengths. This adjustment represents an important part of this invention, as

hereunder described.

In the first place, two brakes are adjusted in order to obtain the same deformation approximately corresponding to the tension required and a short trial length of the pair to be produced, is procured, and the two branches of the said trial pair are then separated in order to compare their lengths- If the. lengths are different, .for instance, owing to some imperfection in the machine or in the brakes, the adjustment of one or the other brake is changed in the direction indicated by the comparison of the lengths and a second trial length is produced. This procedure is continued until two branches of the same length are obtained. This last adjustment of the brakes permits the twisting of the pair to be started without any danger of finding in the finished cable excessive unbalancing values.

It is known that in the case of twisting with great length of twist, the twisted pairs are transformed into two parallel wires which cross periodically. The crossing points can be displaced in consequence of the action of inevitable forces in manufacture, thus rendering irregular the distances of the crossing points. This deterioration of the twisting of the pairs can be avoided by means of a binding tightly wound around the pairs at the moment of twisting of the two wires, this binding being effected by means of a braiding machine mounted on the twisting machine. The application to the present invention of this known process gives results much superior to those obtained in manufacture by the use of winding-off bobbins.

In view of the extremely low value in the differences of lengths to be ascertained, a mechanical law is applied and this application, which had not hitherto been made for that purpose, also represents an integral part of the invention. If any homogeneous flexible rope of a length B is stretched sufiiciently taut between two fixed points situated at the same height and at a distance L from each other, the rope takes substantially the form of a parabola provided that the sag F is small in value. The value of B can be shown mathematically to be a function of the quotient in the form of a continuous series of terms of increasing powers of Bi --Ba=8/3.1/L. (1 1 -15 For instance, for =25 metres, F1=1100 and F2=1000 mm. we have B1B:=22.4 mm., that is to say a difference in the lengths less than 0.1% of the average lengths of the conductors. A difference in the sags of 5 mm. is readily observable. It gives a difference in the lengths of less than 0.005%. It will be seen that the method according to this invention gives a remarkable accuracy with the aid of the simplest means.

If the two sags are of different magnitudes, then either the brake producing the longer core is adjusted to a greater strength or the other brake is adjusted to a less strength. After this adjustment, a new trial length is made and untwisted and the lengths of the component conductors compared in the same way as before. This procedure is repeated until the required adjustment is obtained.

Experience shows that a difference in length of 0.1% results in an unbalancing of inconvenient size in the case of a cable length of 230 metres. The efficiency of this part of the invention is then very considerable. The application of this method of comparison of lengths to the ordinary method of manufacture with unwinding bobbin brakes oii'ers no advantage, because the adjustment of the brakes is not suiiiciently sensitive or sufliciently invariable. In order to use this invention, as above described, the conductors on the bobbins, the ordinary brakes of which are lightly applied, are allowed to unwind. In order to do away altogether withthe influence of these brakes, it is also possible (this is another integral part of the invention) to allow the conductors of the cone around which they are arranged in the form of rings (in the same way as for instance, bare copper wire is supplied from wire mills) to become unwound. In such case the conductor enters almost without tension into the deformation brake and the tension is subjected to no other influence than that of the deformation brake.

The invention ensures not only a cable of superior quality, but it also lowers the cost price. The manufacture is simpler, it does not require .Patent 01 the United States of America is:-

1. In a method of manufacturing electric cables tor signalling which comprise twisted strands of insulated conductors, supporting loosely wound supplies of the strands in coils from below, taking said strands not yet being under tension from said coils and drawing them by equal force through direct brakes coordinated individually to each of said strands, said brakes working by deforming the strands, applying thereby equal tension to each of said strands, and combining and twisting the strands while being under equal tension.

2. In a method of manufacturing electric cables for signalling which comprise twisted groups of twisted strands of insulated conductors, supporting loosely wound supplies of the groups in coils from below, taking said twistedgroups not yet being under tension from said coils and drawing them by equal i'orce through adjustable direct brakes coordinated individually to each of said groups applying thereby equal tension to each of said groups, and combining and twisting said groups while being under equal tension, and unwinding the groups of a trial length and measuring the lengths of the groups, adjusting the brakes if different lengths exceeding predetermined limits are ascertained, so that the differences are reduced below said limits.

MAURUB KLEIN. 

